This invention pertains to the art of joining or bonding and more particularly to adhesively joining or bonding a plurality of superimposed material layers.
The invention is particularly applicable to joining conventional fabric type materials and will be described with particular reference thereto; however, it will be appreciated by those skilled in the art that the invention has broader application and may be advantageously applied in joining other materials such as, for example, leather, synthetics and the like.
As is well known, fabrics are normally interconnected or joined together by a sewing process using conventional sewing machines which employ continuous strands of fabric or synthetic thread which is "stitched" along a desired path. In typical sewing machine operations, a continuous supply of thread is supplied to the sewing needle tip and the needle is then reciprocated through the fabric layers at the area to be joined for cooperation with thread supplied beneath the fabric by a bobbin arrangement. As the needle is reciprocated, the fabric layers are moved in timed relationship with reciprocation of the needle in order that a continuous sewed or stitched area is generated. Even though conventional sewing machines have proved extremely useful when used with fabric and other materials, having become quite sophisticated and capable of performing a number of varied sewing or stitching functions, there are certain inherent disadvantages to these conventional machines.
More particularly, the fabric or synthetic thread employed must be continuously uncoiled from a spool, bobbin or similar apparatus during the sewing or stitching operation. These spools, bobbins and like apparatus so necessary to conventional sewing machine systems are sometimes cumbersome and time consuming to use. In addition, the complexity of conventional apparatus required in order to obtain a particularly desired finished stitch may, in many instances, be quite intricate and thus, susceptible to breakdowns and other maintenance problems. Further, for both aesthetic and practical reasons, the fabric or synthetic thread employed in typical sewing or stitching operations for fabric is very thin and, therefore, not particularly strong. As a result, sewed or stitched joints formed by conventional sewing machines or systems are susceptible to damage or parting when opposed forces are applied to the sewed or stitched area. Also, because of the nature and interconnection of stitches generated by conventional sewing machines, they are susceptible to unraveling.
There have already been various attempts made toward replacing the conventional thread type sewing or stitching systems with systems employing adhesives or other bonding materials. While overcoming at least some of the disadvantages encountered with conventional sewing machines, these prior attempts at adhesive bonding or joining have not proved entirely satisfactory for widespread practical use. Some of these designs were similar to conventional sewing or stitching machines in operation, employing hollow sewing needles with adhesive material forced outwardly therefrom into the material being joined through an orifice disposed at the needle tip. In such an arrangement, the adhesive may tend to dry or become clogged within the needle or adhesive supply lines, thus requiring either needle replacement or cleaning. This, of course, generates undesired machine downtime, and is otherwise inconvenient.
Other prior adhesive bonding apparatus attempt to employ a substantially conventional sewing machine which, through modification, utilize an adhesive reservoir disposed beneath the material to be joined so that the needle is dipped into the adhesive as it reciprocated into and out of piercing engagement with the material to be joined. This type of prior apparatus, however, requires that a very sharp needle be employed and is limited to use with materials having a very minimal thickness or low resistance to piercing by the needle during the joining operation. Further, the strength of those adhesive joints thus generated is suspect inasmuch as it is difficult to insure that the adhesive material is fully dispersed through the material layers at the joining zone or area.